Spectrum analyzer

ABSTRACT

A spectrum analyzer is provided in which a digital recirculating delay line memory is used in conjunction with a swept receiver to effect a time variant signal across a frequency range of interest. The swept receiver is fed analog signals for subsequent analog to digital conversion. Thereafter, a logic circuit simultaneously associated with a delay line memory, sweep receiver circuit and computer receives the converted digital signals. The logic circuit and an analog to digital converter are simultaneously controlled by a common clock. The logic circuit synchronizes the receiver sweep to the recirculating memory and the digital recirculating memory stores in digital format for future utilization the spectral characteristics of the frequency range of interest.

United States Patent Feb. 8, 1972 Sues [54] SPECTRUM ANALYZER [72]inventor: Lawrence B. Sues, Rome, NY.

[73] Assignee: The United States of America as represented by theSecretary of the Air Force A [22] Filed: Sept. 10, 1970 21 Appl.No.:70,971

us. Cl. ..340/17: R, 324/77 c ..Gl1c 21/00,G0lr 23/02 Field of Search..324/77 A, 77 B, 77 C, 77 CS, 324/77 D; 325/332, 333, 336, 363; 340/173R Primary Examiner-Stanley M. Urynowicz, Jr. Attorney-Harry A. Herbert,Jr. and George Fine [57] ABSTRACT A spectrum analyzer is provided inwhich a digital recirculating delay line memory is used in conjunctionwith a swept receiver to effect a time variant signal across a frequencyrange of interest. The swept receiver is fed analog signals forsubsequent analog to digital conversion. Thereafter, a logic circuitsimultaneously associated with a delay line memory, sweep receivercircuit and computer receives the converted digital signals. The logiccircuit and an analog to digital converter are simultaneously controlledby a common clock. The logic circuit synchronizes the receiver sweep tothe recirculating memory and the digital recirculating memory stores in[56] References Cited digital format for future utilization the spectralcharacter stics UNITED STATES PATENTS of the frequency range ofinterest.

3,173,087 3/1965 Loposer ..324/77 X 4Claims, 1 Drawing Figure .6 06 4/3JWFWJ" lat 4'7? V 7mm tame yn-x 2)? .5 1 l J r" 3 10 (ll Isa/Mame a i /lT 9 EJ612141 .8544 SW55) 7 Y (m can" 46f.

(mew/7 Agra/02y (NIP/17H 11 SPECTRUM ANALYZER BACKGROUND OF THEINVENTION are in analog form and generally the signal variations are ofrapid occurrence at rates considerably in excess of a human operatorusing conventional spectrum surveillance equipment. Further the signalsof interest may range over a wide frequency range and limitations existin the prior art in the capability of automatic monitoring thereof.Still further many advantages would be derived from the ability toconvert analog signals of interest to a digital format thus permittingin- .putting to digital devices such as computing machines or digitalrecorders. v

The present invention provides swept electromagnetic spectrumsurveillance equipment with an output suitable for use with digitalinformation processing systems. Some'of the advantages of this spectrumanalyzer are that signal variations of rapid occurrence are efficientlydetected and the output format is compatible with digital dataprocessing equipment and with digitally programmed receivers. Thisinvention is suitable for use in passive electronic reconnaissance andin electromagnetic compatibility instrumentation.

SUMMARY OF THE INVENTION A spectrum analyzer is provided which includesa swept frequency receiver being fed analog signals of interest. Theoutput of the receiver are converted to representative digital signals,by an analog to digital converter. A computer is utilized to initiatethe start of the receiver sweep by means of a programmed pulse therefromthrough a logic circuit to a sweep circuit incorporated as part of thereceiver. A recirculatingdelay line memory is associated with the logiccircuit and receives the digital information-therefrom for purposes ofstorage and further utilization. The analog to digital converter, thelogic circuit and in turn the delay line memory are controlled by acommon clock for synchronization purposes. By programmed command of thecomputer, the stored digital information representative of the spectralcharacteristics of the analog signal may be read out from therecirculating digital delay line to the computer for further processingor comparison to other similar stored preceding signals for detection ofvariations between signals.

An object of this invention is to provide a spectrum analyzer receivingan analog signal and providing an improved method for obtaining thespectrum characteristics in digital format.

Another object of this invention is to provide a spectrum analyzerincluding a digital recirculating delay line memory operating inconjunction with a swept receiver to effect a time variant signal acrossa frequency range of interest.

Yet another object of this invention is to provide a spectrum analyzerusing a digital recirculating memory to store a digital format thespectral characteristics of the frequency range of interest.

Still another object of this invention is to provide a spectrum analyzerin which a receiver sweep is synchronized to a recirculatingmemory foruse with fixed delay memories.

A further object of this invention is to provide a spectrum analyzerwherein stored spectral data is used for online comparison to subsequentspectral activity by digital circuitry to generate discrete signals whena variation of activity in the frequency range being analyzed occurs.

DESCRIPTION OF DRAWINGS There is shown a single FIGURE illustrating inblock diagram form the spectrum analyzer of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENT Referring in detail to the singleFIGURE of the present invention, there is shown preselector 1 receivingat input In an analog electromagnetic signal such as from a jammer,radar or communications network. Preselector l is arranged so as to beautomatically tunable over a predetennined frequency range by a sweepvoltage signal applied to input 5. Preselector l is conventional and maybe electromagnetically tuned by conventional ferromagnetic means. Theoutput of preselector 1 is fed to log amplifier 6 by way of mixer 2 thusproviding a preselected intermediate frequency. It is noted that mixer 2receives a local oscillator signal from local oscillator 3 which is avoltage controlled oscillator which may be varied in frequency also overa predetermined frequency range by applied sweep voltage signal. Sweepcircuit 4 is utilized to provide a common predetermined sweep voltagesignal to be applied to both preselector l and local oscillator 3. The

aforesaid predetermined sweep voltage signal is applied to preselector lby way of driver 5. Sweep circuit 4 is designed to receive an initiatingsignal from logic circuit 9 to start each sweep voltage signal. Thus,local oscillators and preselector l are simultaneously. andautomatically tuned over a predetermined frequency range by a commonsweep voltage signal initiated at a predeterrrnined time. Thecombination of preselector l, mixer 2, local oscillator 3, sweep circuit4 and driver 5 comprises an automatically tuned swept receiver.

Log amplifier 6 is utilized to provide a greater dynamic range and theoutput thereof are analog signals. Analog to digital converter 7receives analog signals from log amplifier 6 and provides at the outputthereof representative digital signals. Analog to digital converter 7receives a timing signal from clock 8 thereby permitting a predeterminedsampling from analog to digital converter 7. The digital signalsrepresentative of the input analog signals are fed to digital logiccircuit 9. Clock 8 also controls digital logic circuit 9 and thus at apredetermined time the digital signals are fed from logic circuit 9 torecirculating delay line memory 10. Thus clock 8 also controls by way ofdigital logic circuit 9 the operation of delay line memory 10.

Digital computer 11 is programmed so that a predetermined pulsetherefrom is transmitted to digital logic circuit 9 which will provide astart pulse to sweep circuit 4. Thereupon preselector 1 and localoscillator 3 will automatically sweep over a predetermined frequencyrange to effect a swept receiver operationflhe output from clock 8synchronizes the operation of analog to digital converter 7, digitallogic circuit 9, and recirculating delay line memory 10. The serialmemory of delay line 10 now in digital form stores the amplitude offrequency spectrum of interest. Computer 11 is also programmed so thatat a predetermined command the stored digital information may be readout to computer 11 for rapid utilization thereof. Computer 11 is alsoprogrammed to store preceding digital signals of interest to compareagainst sub sequent digital signals of interest and thus pernnit the useof stored spectral data for online comparison to subsequent spectralactivity to generate discrete signals when a variation of the activityin the frequency range being analyzed occurs. It is noted that digitallogic circuit 9 is conventional and may be of the type associated with aconventional digital computer such as computer 1 1. In the alternativedigital logic circuit 9 may be associated with delay line memory 10which combination is conventional as manufactured and sold by AndersenCo.

It is emphasized the present invention may be utilized as a signalactivity processor to provide swept electromagnetic spectrumsurveillance equipment with an output for use with digital informationprocessing systems. The unique advantages of this processor are thatsignal variations of rapid occurrence are efficiently detected at ratesconsiderably in excess of the capability of a human operator usingconventional spectrum surveillance equipment and that the output formatis compatible with digital data processing equipment and with digitallyprogrammed receivers.

it is also noted that this invention used as a signal activity processoris readily adaptable to sequential detection processes using variablesignal observation periods. When used in this manner, the output of thesequential detector would also serve as the clock for digital circuitryand a shift register would be used for the delay line memory.

I claim:

1. A spectrum analyzer comprising a swept receiver being fed analogelectromagnetic signals of interest, said swept receiver beingautomatically tunable over a predetermined frequency range, means toconvert the analog output signals from said swept receiver torepresentative digital signals, recirculating delay line means, adigital logic circuit receiving said representative digital signals fromthe analog to digital converting means for predetermined timed storagein said recirculating delay line means, common clock means for saidanalog to digital converting means and said digital logic circuit forsynchronizing their operation and in turn that of said recirculatingdelay line means for predetermined time serial storage of the digitalsignals, a sweep circuit providing a predetermined sweep voltage signalfor application to said swept receiver for automatic tuning thereof oversaid predetermined frequency range, and a digital computer programmed totransmit a predetermined timed signal by way of said digital logiccircuit to said sweep circuit for initiation of said application of saidpredetermined sweep voltage signal to said swept receiver, said digitalcomputer also being programmed to issue a command by way of said digitallogic circuit to said recirculating delay line means to read out theretothe stored digital signals for further utilization thereof.

2. A spectrum analyzer as described in claim 1 further including a logamplifier interconnecting said swept receiver and said analog to digitalreceiver to provide a wide dynamic range.

3. A spectrum analyzer as described in claim 2 wherein said sweptreceiver is comprised of means receiving said analog electromagneticsignals, said means being automatically tunable over a predeterminedfrequency range upon the receipt of said sweep voltage signal from saidsweep circuit a mixer interconnecting said tunable receiving means andsaid log amplifier, a voltage controlled local oscillator tunable over apredetermined frequency range also upon the receipt of said sweepvoltage signal from said sweep circuit.

4. A spectrum analyzer as described in claim 3 including a driverreceiving said sweep voltage signal from said sweep circuit prior to theapplication to said tunable receiving means.

1. A spectrum analyzer comprising a swept receiver being fed analogelectromagnetic signals of interest, said swept receiver beingautomatically tunable over a predetermined frequency range, means toconvert the analog output signals from said swept receiver torepresentative digital signals, recirculating delay line means, adigital logic circuit receiving said representative digital signals fromthe analog to digital converting means for predetermined timed storagein said recirculating delay line means, common clock means for saidanalog to digital converting means and said digital logic circuit forsynchronizing their operation and in turn that of said recirculatingdelay line means for predetermined time serial storage of the digitalsignals, a sweep circuit providing a predetermined sweep voltage signalfor application to said swept receiver for automatic tuning thereof oversaid predetermined frequency range, and a digital computer programmed totransmit a predetermined timed signal by way of said digital logiccircuit to said sweep circuit for initiation of said application of saidpredetermined sweep voltage signal to said swept receiver, said digitalcomputer also being programmed to issue a command by way of said digitallogic circuit to said recirculating delay line means to read out theretothe stored digital signals for further utilization thereof.
 2. Aspectrum analyzer as described in claim 1 further including a logamplifier interconnecting said swept receiver and said analog to digitalreceiver to provide a wide dynamic range.
 3. A spectrum analyzer asdescribed in claim 2 wherein said swept receiver is comprised of meansreceiving said analog electromagnetic signals, said means beingautomatically tunable over a predetermined frequency range upon thereceipt of said sweep voltage signal from said sweep circuit a mixerinterconnecting said tunable receiving means and said log amplifier, avoltage controlled local oscillator tunable over a predeterminedfrequency range also upon the receipt of said sweep voltage signal fromsaid sweep circuit.
 4. A spectrum analyzer as described in claim 3including a driver receivinG said sweep voltage signal from said sweepcircuit prior to the application to said tunable receiving means.